1. Field of the Invention
This invention generally relates to a sheet material dispenser of the type wherein a user, for each use, manually grasps a free leading end portion of a supply of a limp, non-self-supportable, thin, broad, sheet material such as plastic film, and withdraws a desired length of the same to be dispensed and, more particularly, to a frictional drag arrangement for tensioning the sheet material to render the same taut during each withdrawal, particularly when the sheet material supply is almost completely spent.
2. Description of the prior art
Dispensers for dispensing sheet materials such as plastic film, metal foil, waxed paper, tissue paper, paper or like wrapping stock have been well known for both domestic and commercial purposes. For commercial wrapping purposes, plastic film, for example, was generally wound about a tubular core mounted for rotation in a box that rested flatly on a supporting surface such as a work table or countertop. The plastic film was typically furnished in large-sized and large-capacity rolls having film lengths of 500 ft. and more, and film widths on the order of 12" and more. A free leading end portion of the sheet material was generally grasped by a user with one or both hands, who then manually pulled and withdrew the material in a taut state from the box, and thereupon urged the taut material against a fixed, constantly-exposed cutter strip that was conveniently provided on the box, usually along one of the outer edges or walls of the same. The cutter strip typically had a serrated cutting edge constituted of a row of generally triangularly-shaped teeth.
As described in currently pending U.S. patent application Ser. No. 633,019, filed July 20, 1984, and owned by the same assignee as the instant invention, there were many problems associated with the aforementioned prior art dispensers, as well as other types of dispensers. It was an object of the dispenser described in said patent application to overcome those prior art problems and, in the preferred embodiment of the dispenser described in said application, a roll of sheet material was coiled around a cylindrical tubular core journaled for rotation within a housing. A free leading end portion of the sheet material was grasped by a user who pulled and manually withdrew the sheet material out from the housing. A drag was exerted on the sheet material during its withdrawal to tension the same. The drag was caused, in part, by the inertia of the coiled roll, and the friction of the sheet material engaged with various portions of the dispenser. The taut film was initially guidably moved transversely past and spaced from a cutting element mounted on the support, and thereupon the taut film was moved onto the cutting element. The cutting element was protected by a guard element also mounted on the support, and said elements were moved relative to each other in response to the movement of the taut film to expose the cutting element and cut the withdrawn sheet material moved thereonto.
The dispenser described in the aforementioned patent application proved to be extremely satisfactory for its intended purpose. In order to even further improve the efficiency of the dispensing operation, it was desirable to ensure that each successively withdrawn length of sheet material was taut, even when the sheet material was almost completely spent from the roll. The magnitude of the aforementioned drag force decreased in value as more and more of the sheet material was unwound from the roll, because the weight of the coiled roll decreased with use. Thus, a fresh roll consisting of 1000 ft., 2000 ft., 3000 ft. and more, of plastic film, and having a width on the order of 12" or 18" and more, weighed several pounds and, together with other factors, exerted a considerable drag force when one withdrew the leading end portion of the material. However, toward the end of the roll, for example, when there was about 100 ft. or less of film remaining, the weight of the roll was considerably less, and the drag force contributed by the weight of the roll was proportionally lower. At the end of the roll in the dispenser described in said application, it sometimes happened that the drag force contributed by the weight of the roll was insufficient to exert a proper tension on the withdrawn film. Also, it was believed to be advantageous to compensate somewhat for the large differential in said drag force, due to the large differential in the weight of the roll between the beginning and end of each roll, and it was also deemed advantageous to maintain the overall drag force on the trailing end portion of the sheet material more uniform over successive dispensing operations of the roll.